1. Field of the Invention
This invention relates to an optical fiber connecting apparatus for interconnecting optical fibers in series, an electronic equipment, a network system and an optical fiber connecting method. More particularly, it relates to an optical fiber connecting method, an electronic equipment, a network system and an optical fiber connecting method which can be used with advantage for interconnecting optical fibers in constructing an optical fiber network.
2. Description of the Prior Art
There is an optical fiber network by so-called light communication in which e.g., digital signals are transmitted using an optical fiber. In e.g., an optical fiber network, it is possible to interconnect e.g., household electrical products or information equipments with one another.
Heretofore, an optical fiber is formed of glass. With the advent of the plastic optical fiber (POF), it has become possible to construct an optical fiber inexpensively in homes of offices. The inexpensive structure or the optical fiber network leads to creation of new businesses in the field of utilization of advanced household electrical appliances.
In transmitting signals using an optical fiber, there are known two methods, namely a bi-core type bidirectional optical communication employing two optical fibers, and a bidirectional optical communication employing a sole optical fiber.
In the bi-core type bidirectional optical communication, one of the optical fibers is used for transmission, with the outer being used for reception. On the other hand, the uni-core type bidirectional optical communication uses a sole optical fiber to effect signal transmission/reception, so that the optical fiber cost in constructing the network is one-half that for the bi-core system. Also, with the bi-core system, the two fibers are intended for separate purposes, that is for transmission and for reception, thus leading to directive coupling between the light transmission/reception apparatus and the optical fibers.
The optical fiber is connected to an optical fiber connecting portion provided in the optical transmission/reception apparatus. The optical fiber connection portion of the optical transmission/reception apparatus of the bi-core system is divided into a transmitting side connecting portion for transmitting optical signals and a reception side connecting portion receiving optical signals. Thus, in transmitting/receiving optical signals, the optical signal flowing direction through each optical fiber is necessarily unidirectional. That is, in the optical fiber network, performing optical communication between the first and second optical transmission/reception devices the transmitting side connecting portion of the first optical transmission/reception device needs to be connected by an optical fiber to the receiving side connecting portion of the second optical transmission/reception device. Similarly, the receiving side connecting portion of the first optical transmission/reception device needs to be connected by an optical fiber to the transmitting side connecting portion of the second optical transmission/reception device. If the bi-core system is used, the optical fibers need to be connected in association with respective connecting portions.
On the other hand, the uni-core type bidirectional optical communication is superior in system construction since it does not suffer the aforementioned problem of directivity to assure facilitated connection of the first and second optical transmission/reception devices to the optical fiber connecting portions.
The uni-core bidirectional optical communication recently is stirring up notice in that the amount of the optical fibers used can be decreased and connection to optical fibers is facilitated.
Meanwhile, the uni-core type bidirectional optical communication suffers from the problem of so-called cross-talk.
The cross-talk means the problem that optical signals from a sending party become mixed into optical signals from the optical signal transmission/reception device connected to the sending device over an optical fiber. Among the factors contributing to the cross-talk is a mechanism in which the light transmitted by the sending party is reflected by the remote end of the optical fiber connected to the other optical fiber to prove the remote-end-reflected light which then falls on the light receiving section of the sending device. The reflection at the remote end of the optical fiber, termed Fresnel reflection, is brought about by the properties of light that it is reflected by an interface between two mediums of different refractive indices.
In general, the optical fibers suffers losses, such that, if optical signals are transmitted over an optical fiber, the optical signals are decreased in amplitude. That is, loss in light volume is produced by optical fiber transmission. Therefore, if the optical fiber is of an increased length, the light reflected on the remote end is of a reduced light quantity, due to optical fiber loss, when it returns to the light receiving portion of the own device, thus the effect of the optical crosstalk being reduced. However, if the optical fiber is of an decreased length loss in the light volume by optical fiber transmission is only small, thus increasing the effect of cross-talk by the reflected light from the light receiving portion.
In particular, if a first light transmission/reception device 201 is interconnected to a second light transmission/reception device 202 over a short optical fiber 203 and a long optical fiber 204, coupled together, remote end reflection poses a serious problem. In the structure shown in FIG. 1, the optical fibers 203, 204 are coupled to each other by a connector 205. By using the connector 205, made up of a first connecting member 206 and a second connecting member 207, detachably connected to each other, the first connecting member 206, provided in the vicinity of an end face of the optical fiber 203, and the second connecting member 207, provided in the vicinity of an end face of the optical fiber 204, are connected to each other to connect the end face of the optical fiber 203 to the end face of the optical fiber 204.
Referring to FIG. 2, the amplitude attenuation in the optical signals transmitted over the optical fibers 203, 204 interconnected by the connecting portion 208 is explained.
Referring to FIG. 2A, light S transmitted from the first light transmission/reception device 201 is reflected by the connecting portion 208 on the end face of the optical fiber so as to fall as remote end reflected light FX on the first light transmission/reception device 201. For example, the remote end reflected light Fx falls with an amplitude BFX on the first light transmission/reception device 201.
On the other hand, in FIG. 2B, the first light transmission/reception device 201 receives light D of an amplitude BD sent over optical fibers 203, 204 from the second light transmission/reception device 202.
It is noted that arrows A in FIGS. 2A and 2B indicate the direction in which occurs the loss in the optical fiber.
If, for example, the amplitude BFX of the remote-end-reflected light FX is close to the amplitude BD of the received light D, the first light transmission/reception device 201 cannot distinguish the remote-end-reflected light FX from the received light D sent from the second light transmission/reception device 202, thus producing the aforementioned problem of cross-talk.
As a matter of course, the amplitude of the optical signals and the remote-end-reflected light depends on the length of the optical fiber, the number of optical fibers to be interconnected, and on the light emission intensity of the optical transmission/reception apparatus. This poses a serious problem for the light transmission/reception apparatus of the uni-core bidirectional system in an optical fiber network constructed by optical fibers of variable lengths.
As a pertinent technique of prohibiting Fresnel reflection on the connecting portion 208, there is known such a method in which an end face 213a of an optical fiber 213 and an end face 214a of an optical fiber 214 are polished to round shape to high precision to abut the cores against each other, as shown in FIG. 3.
In this method, the end faces 213a, 214a of the optical fibers 213, 214 are interconnected by the connector 215. Specifically, a first connecting member 216 is mounted in the vicinity of the end face 213a of the optical fiber 213, a second connecting member 217 is mounted in the vicinity of the end face 214a of the optical fiber 214 and the connecting members 216, 217 are fitted to a substantially annular fitting member 218 to interconnect the optical fibers 213, 214.
This method has, however, a drawback that the end faces need to be machined to high precision, thus increasing the cost. There are also problems that the connection becomes invalid if an air layer is interposed between the optical fiber 213, 214, and that, if vibrations are applied to the optical fibers 213, 214, the end faces 213a, 214a rub against each other to produce scratches. If scratches are produced due to rubbing, transmission of the signal light becomes impossible in the worst case.
FIG. 4 shows a method of interconnection of optical fibers in which an optical adhesive 222 is used to prevent remote end reflection from occurring. In this method, a first connecting member 226 is mounted in the vicinity of an end face 223a of the optical fiber 223, whilst a second connecting member 227 is mounted in the vicinity of an end face 224a of the optical fiber 224, these connecting members 226,227 being fitted to the ring-shaped fitting member 228. The end face 223a of the optical fiber 223 is bonded to the end face 224a of the optical fiber 224 by the optical adhesive 222 having a refractive index close to that of the cores 223b, 224b of the optical fibers 223, 224, thereby prohibiting the reflection from the remote end. However, since the optical fibers are bonded to each other, difficulties are met in re-dismounting the optical fibers. Meanwhile, the diameters of the core 223b, 224b of the optical fibers of quartz 223, 224 are approximately 5 xcexcm in diameter, with the diameters thereof inclusive of clad layers 223c, 224c being approximately 125 xcexcm.
It is therefore an object of the present invention to provide optical fiber connecting method and apparatus in which optical cross-talk is prevented from occurring to assure optical communication in accordance with the uni-core bidirectional system.
In one aspect, the present invention provides an optical fiber connector for interconnecting a first optical fiber and a second optical fiber including refractive index matching means having a refractive index subsequently equivalent to that of cores of first and second optical fibers, and optical fiber connecting means for interconnecting the first and second optical fibers in a state in which end faces of first and second optical fibers are contacted with refractive index matching means interposed between first and second optical fibers.
In another aspect, the present invention provides a network system for interconnecting a plurality of electronic equipments including a first electronic equipment including a first optical communication circuit, an optical fiber connector, a first fiber for interconnecting first optical communication circuit and optical fiber connector, a second electronic equipment having a second optical communication circuit and a second optical fiber for interconnecting the optical fiber connector of first electronic equipment and second optical communication circuit of second electronic equipment. The optical fiber connector of first electronic equipment includes refractive index matching means having a refractive index substantially equivalent to that of cores of first and second optical fibers and optical fiber connecting means for interconnecting first and second optical fibers in a state in which end faces of first and second optical fibers are contacted with refractive index matching means interposed between first and second optical fibers.
In still another aspect, the present invention provides a electronic equipment having an optical communication circuit. The electronic equipment includes an optical fiber connector, and an optical fiber for interconnecting optical communication circuit and optical fiber connector. The optical fiber connector includes refractive index matching means, at an end of optical fiber, having a refractive index substantially equivalent to that of cores of first and second optical fibers, and optical fiber connecting means for interconnecting optical fiber and another optical fiber in a state in which end faces of optical fibers are contacted with refractive index matching means interposed between optical fibers.
In yet another aspect, the present invention provides a method for interconnecting a first optical fiber and a second optical fiber. The method includes a step of interposing refractive index matching means having a refractive index substantially equivalent to that of cores of first and second optical fibers between an end face of first optical fiber and an end face of second optical fiber, and a step of interconnecting first and second optical fibers in a state in which end faces of first and second optical fibers are contacted with refractive index matching means.
In the optical fiber connecting apparatus, according to the present invention, the end faces of the two optical fibers are interconnected in a state in which the end faces are contacted with refractive index matching means interposed therebetween.
That is, with the optical fiber connecting apparatus, the optical fiber connector interconnects the optical fibers in a state in which the end faces are contacted with the refractive index matching means.
In this manner, with the optical fiber connecting apparatus, product costs can be lowered without the necessity of observing machining accuracy in polishing the end faces of the optical fibers, while optical signals can be transmitted in a manner suited for optical communication, with the optical fibers being interconnected and detached from each other as desired.
In the optical fiber connecting method, according to the present invention, the end faces of the two optical fibers are interconnected in a state in which the end faces are contacted with refractive index matching means interposed therebetween.
That is, with the optical fiber connecting method, the optical fiber connector interconnects the optical fibers in a state in which the end faces are contacted with the refractive index matching means.
In this manner, with the optical fiber connecting method, product costs can be lowered without the necessity of observing machining accuracy in polishing the end faces of the optical fibers, while optical signals can be transmitted in a manner suited for optical communication, with the optical fibers being interconnected and detached from each other as desired.